It is known to recover the preponderance of vaporized solvent from reaction off-gas by passing it through at least one cooling, absorbing, and/or distillation means to produce a liquefied recovered solvent. It is generally desirable to maximize the recovery from reaction off-gas of vaporized compounds containing at least one hydrocarbyl bond, herein called “hydrocarbyl compounds,” “volatile organic compounds,” and “VOC”.
It is known to use at least one distillation means to remove from recovered solvent an amount of excess water, which is coproduced in large quantities by the partial oxidation of pX. Various designs are known for using energy derived from the partial oxidation of pX for at least a portion of the energy input required to operate a distillation means.
The term “water of TPA formation” is defined herein as 0.340 kilogram of water per kilogram of commercial purity pX feed. This comes from the intended reaction forming TPA from pX according to the stoichiometry: pX+3 O2 yields TPA+2 H2O. Notwithstanding that small amounts of impurities exist within commercial purity pX and that a small amount of pX is under-oxidized and/or over-oxidized, modern manufacturing facilities produce commercial purity pX comprising very low amounts of impurities and to convert such feed into crude and/or purified TPA with very high yields. Preferably the overall yield of TPA solid product, crude and/or purified, is at least about 96, or 97, or 98, or 99 mole percent based on the mass of commercial purity pX feed divided by a molecular weight of 106.16 grams per mole. Preferably, the commercial purity pX feed comprises at least about 0.990, or 0.995, 0.997, or 0.998 mass fraction of pX.
It is also known to recover energy, both thermal energy and mechanical shaft work, from a portion of off-gas in various combinations along with recovery of vaporized solvent. One known method for energy recovery is to use at least a portion of off-gas to boil a working fluid, e.g., water or pentane, to produce a vapor. This vapor is used to transfer heat to another user, or the vapor is reduced in pressure through an expander, typically a turboexpander, to produce shaft work output. The energy recovery from a turboexpander can be converted directly to mechanical work, such as driving an air supply compressor or other moving machinery, or to electrical power by driving a rotating electrical generator connected to a power distribution and consuming network.
Another known method for energy recovery is to pass at least a portion of the off-gas comprising dinitrogen through a turboexpander. The energy recovery from a turboexpander can be converted directly to mechanical work, such as driving an air supply compressor or other moving machinery, or to electrical power by driving a rotating electrical generator connected to a power distribution and consuming network.
It is also known to send a significant portion of water in vapor form in the off-gas to a thermal oxidative destruction means (TOD) wherein noxious gaseous and VOC pollutants, e.g., carbon monoxide, acetic acid, methyl acetate, para-xylene, and methyl bromide, are converted to more environmentally acceptable effluents, e.g., water vapor and carbon dioxide. Certain convention systems disclose expelling “the water of reaction” in vapor form from a para-xylene oxidation reactor into a thermal destruction device for removal of noxious pollutants.